Some astronomers suggested the existence of a still-undiscovered world in the outer regions of the solar system to explain orbital anomalies of asteroids and comets at the edge of the solar system.

Planet 9

Scientists hypothesized this world could be about five times the size of the Earth and orbits the sun at a distance between 300 and 1,000 AU. The so-called Planet 9, however, remains elusive and has not yet been found.

In a new paper, astronomers Jakub Scholtz of Durham University and James Unwin of University of Illinois at Chicago, proposed the possibility that this elusive world may not be a planet as popularly believed.

They said this mysterious object could be a primordial black hole.

Primordial Black Holes

The existence of primordial black holes has not yet been proven, but they are believed to be old black holes that formed soon after the Big Bang. Scientists also think this type of black hole could be as small as an atom but has a mass comparable to that of a large mountain.

Scientists think primordial black holes formed due to density fluctuations in the very early universe. Those with lower mass likely evaporated but the ones with larger masses may still exist.

Bowling Ball-Sized Primordial Black Hole

Researchers said that while the widely accepted explanation for the strange phenomena in the outer regions of our star system is a free-floating planet, they argued that it is also possible these are caused by a primordial black hole.

"We take these objects to be primordial black holes (PBHs) and point out the orbits of TNOs would be altered if one of these PBHs was captured by the Solar System, inline with the Planet 9 hypothesis," they wrote in their study.

Researchers think that the primordial black hole that could be lurking still undiscovered in the solar system could be five times more massive than Earth and has a radius of just about 5 centimeters, or about the size of a bowling ball, which would make it difficult to find.